There are known screw extruder-calender assemblages in which the effect of variations of the extruder output are equalized by providing between the output end of the extruder and the input side of the calender rolls wall portions which extend from the extruder end to the calender rolls within the input range thereof. Equalization means of this kind have not been found satisfactory for several reasons which will be pointed out hereinafter.
The transfer of the extruder output to the calender rolls must be continuous and with a uniform supply of material as otherwise the quality of rolled-out plates and sheets or foils is affected and thus also the results of subsequent processing of the rolled-out material.
The input space provided between the discharge end of the extruder and the calender rolls serves to effect a uniform transfer of material and also a uniform width of the rolled-out material. If now an increase of the extruder output occurs, the uniformity of the rolled-out material is adversely affected and there is also the danger of overloading of machinery in the assemblage by temporary pressure build up in the input space.
The output of the extruder even if the rpm of the extruder screws remains the same, generally does not remain constant but is subjected to variations. Equalization devices as now known provide means which are designed to equalize the quantities of extruded material within a given time unit.
According to published German patent application 1,704,640 (DT-As 1,704,640) a screw extruder-calender combination is provided with a flexible connection between a displaceable frame structure for the rolls and the screw extruder. Such flexible connection serves to compensate by yielding possible excess pressure between the discharge end in the extruder and the input side of the calender rolls.
An equalization device of this type is inherently complex and thus likely to have frequent breakdowns. It is particularly disadvantageous that due to displacement of the frame structure mounting the calender rolls, the lateral limitation of the input range of the calender rolls retracts whereby the effective length of the working gap of the calender is uncontrollably enlarged. Variations in the width of the working gap results in corresponding changes in the width of the rolled-out plates and sheets or foils which in turn causes difficulties with the subsequent operations to which the output of the calender is to be subjected.
According to German patent 971,776 (DT-PS 971,776) equalization of pressure changes in the feed of material is effected by providing at lateral circularly curved cut-outs of the side walls of the discharge end of the extruder sensors which sense the rolled-out material emerging from the cut-outs. As a result of such sensing, the drive for devices used for further processing of the rolled-out material is controlled corresponding to sensed changes in the output.
Such mode of equalization has the disadvantage that a continuously irregular run is effected, not only of the extruder but also of the calender rolls. Moreover, it is necessary also to regulate the running of the devices used for further processing the rolled-out material.